1. Field of the Invention
This invention relates to a radio receiver that displays characters on a display means on the basis of character data signals extracted from a broadcast radio wave which is transmitted by RDS (Radio Data System; FM Character-Multiplex broadcasting system).
2. Description of the Prior Art
There is already known a radio system (RDS) which provides a service wherein when an ordinary radio station broadcasts a program, the information associated with program contents, is transmitted as data through multiplex modulation, thereby permitting the radio listeners to select program contents of their preference on the basis of the data demodulated at the receiver.
With this radio data system, a subcarrier of 57 KHz, which resides outside the band occupied by the FM modulation signal and which is the third harmonic of a 19 KHz stereo pilot signal, is amplitude modulated by a data signal which is filtered and biphase-coded, representative of the program contents to thereby provide radio data signals. A main carrier wave is frequency modulated by this amplitude modulated subcarrier, and then the main carrier is broadcast.
As apparent from FIG. 6, a base band coding structure of the radio data signal consists of 104 bits to form one group and is multiplex transmitted in a repeated manner. One group consists of four blocks, each including 26 bits, and each block consists of a 16-bit information word and a 10-bit check word.
In FIG. 6, block 1 is assigned a program identity code (PI), block 2 a traffic program identity code (TP), block 3 a station frequency (AF) of a network station which is broadcasting the same program as the station currently being received and block 4 program service name information data (PS) such as station name or network name.
Further, the above each group is distinguished by first 4 bits into 16 types, i.e. type 0 to type 15 differing in contents. Further, two versions, version A and version B are defined with respect to respective types (0 to 15) depending on whether the value of the next bit is respectively either 0 or 1. These identification codes are located in block 2. The station frequency (AF) code of the network stations is arranged to be transmitted only by type 0, group A, that is, the case in which the value of first 5 bits in block 2 are all 0, and the program service name (PS) information data is arranged to be transmitted by both type 0, group A and type 0, group B, in other words, either when the value of the first 5 bits are all 0, or when that of first 4 bits are 0 and of the fifth bit is 1.
In this manner, the radio data of the type 0, group A contains the station frequency (AF) data of the network stations which are broadcasting the same program as the station currently being received. When the broadcast wave is received, the station frequency (AF) data obtained by demodulating the broadcast wave is read and is then stored, and by this operation, when the receiving sensitivity of the station currently being received has become poor due to disturbances such as decreasing signal strength, another network station can be selected instead on the basis of the station frequency (AF) data of the network stations stored previously, thereby always permitting the radio listeners to listen to the same program with a good receiving condition free from disturbances.
On the other hand, the program service name information (PS) data is composed of eight or less than eight characters such as English characters, wherein as shown in FIG. 7 which shows a type drawing of a format of the type 0 group A, 16 bits (8 bits.times.2) representing two characters are transmitted by one group, so that eight characters are transmitted by four groups, and in addition, it is determined by the contents of version codes C1 and C0 of the block 2 that which of the eight characters the character in the group being transmitted is.
Further, a character data signal is discriminated whether it represents a capital letter (such as "A" in English Alphabet) or a small letter (such as "a" in English Alphabet) by, for example, the ASCII code, and thereafter it is displayed on a display device. However, if the display device adopted here has to be a cheap and simple one, it is normally constructed such that a character to be indicated is displayed in the capital letter form regardless of whether the character data signal represents a capital letter or a small letter.
Since conventionally used radio receivers are constructed as above, that is, since capital letters only are displayed on a display device, even if the display device can be of a cheap and simple construction, the letters displayed thereon cannot be discriminated whether they represent capital letters or small letters.